Method of improving the quality of diesel fuel

ABSTRACT

In a method of improving the quality of diesel fuel, an oxidizing gas is formed into sub-micron size bubbles which are dispersed into diesel fuel, after which the treated fuel is recovered. The oxidizing gas is preferably ozone and is utilized immediately upon its manufacture. By means of the method, sulfur is removed from the diesel fuel and the cetane rating thereof is increased.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of application Ser.No. 09/418,445 filed Oct. 15, 1999, currently pending, which is acontinuation-in-part of application Ser. No. 09/325,503 filed Jun. 3,1999, now U.S. Pat. No. 6,103,130.

TECHNICAL FIELD

[0002] This invention relates generally to the treatment of contaminatedliquids with oxidizing gases, and more particularly to a method ofimproving the quality of diesel fuel by removing sulfur compoundstherefrom and raising the cetane number thereof.

BACKGROUND AND SUMMARY OF THE INVENTION

[0003] Domestic diesel fuel contains, at most, 0.05% sulfur by weight.Refineries produce diesel fuel as a distillate of crude oil which isthen hydrotreated to reduce the sulfur content to 0.05% or less. Inhydrotreating, a reducing process, the diesel fuel is contacted withhigh pressure hydrogen gas in the presence of a solid catalyst. Thecatalyst serves to remove the sulfur in the form of sulfide, while thehydrogen serves to saturate the molecules from which the sulfur isremoved.

[0004] While hydrotreating is effective at reducing the sulfur contentof diesel fuels substantially, certain forms or sulfur are easier toremove then others. For example, sulfur in the form of sulfide is easierto remove than sulfur in the thiophene form. As a result, the sulfurthat remains in diesel fuel after hydrotreating is mostly in thethiophene form. As thiophenes increase in complexity, the sulfur becomesmore difficult to remove, requiring hydrotreating at more severeconditions. The higher the severity of the hydrotreating process, theshorter catalyst life time. Additionally, severe hydrotreatingconditions lead to cracking of the diesel fuel molecules and thus higheryield losses. The sulfur remaining in diesel fuel after hydrotreating isprimarily or exclusively in the thiophene form. Thiophenes reducedduring the hydrotreating process are converted to biphenyl derivatives.

[0005] Recently, the United States Environmental Protection Agency (EPA)promulgated regulations sharply reducing the allowed sulfur content ofdiesel fuels. No later than year 2006, diesel fuel must contain lessthan 15 ppm sulfur (0.0015% by weight). This standard will requirehydrotreating under conditions of increased severity.

[0006] Diesel fuel quality is rated by cetane number, a parametersimilar to the octane rating number for gasoline. The higher the cetanenumber, the higher the quality of the diesel fuel. One class ofcompounds that contributes to a low cetane number are aromatics,including biphenyl derivatives. Thus, when hydrotreating is used toremove sulfur from diesel fuel, thiophenes are converted to biphenylderivatives and the cetane number of the fuel is reduced.

[0007] In accordance with the present invention, sulfur in diesel fuelis oxidized to a sulfoxide or a sulfone. Once in the sulfoxide orsulfone form, the sulfur-containing molecule is easily removed from thediesel fuel by distillation or extraction. In contrast to hydrotreating,oxidative desulfurization and the subsequent removal of the moleculescontaining the oxidized sulfur results in a decrease in aromaticcontent. The decrease in aromatic content leads directly to an increasein cetane number.

[0008] In accordance with the one aspect of the invention, oxidizing gasis utilized at its source and is formed into sub-micron size bubbleswhich are immediately dispersed into flowing diesel fuel. Due to thesub-micron size of the bubbles, the surface area of the oxidizing gas isgreatly increased, thereby greatly increasing the efficiency of theoxidation reaction.

[0009] In accordance with another aspect of the invention, the oxidizinggas is formed into sub-micron size bubbles by directing it through asintered glass, sintered ceramic, or porous ceramic tube. Diesel fuel iscaused to flow past the exterior of the sintered/porous tube. Theflowing diesel fuel cleaves sub-micron size bubbles of the oxidizing gasfrom the surface of the tube. The sub-micron size bubbles of oxidizinggas are dispersed into the diesel fuel, whereupon sulfur compoundscontained within the diesel fuel are efficiently oxidized intosulfoxides or sulfones, which are in turn removed by distillation orextraction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete understanding of the invention may be had byreference to the following Detailed Description when taken inconjunction with the accompanying Drawings, wherein:

[0011]FIG. 1 is a flow chart illustrating a first embodiment of theinvention;

[0012]FIG. 2 is a diagrammatic illustration of a first apparatus usefulin the practice of the method of the invention;

[0013]FIG. 3 is a diagrammatic illustration of a second apparatus usefulin the practice of the method of the invention;

[0014]FIG. 4 is a diagrammatic illustration of a third apparatus usefulin the practice of the method of the invention;

[0015]FIG. 5 is a diagrammatic illustration of a second embodiment ofthe invention; and

[0016]FIG. 6 is a further illustration of the embodiment of FIG. 5.

DETAILED DESCRIPTION

[0017] Referring now to the Drawings, and particularly to FIG. 1thereof, there is shown a method of improving the quality of diesel fuelcomprising the preferred embodiment of the invention. The first step ofthe method comprises the manufacture of an oxidizing gas utilizingconventional and well known techniques. The oxidizing gas preferablycomprises ozone, however, other oxidizing gases may be utilized in thepractice of the invention, if desired. Immediately upon its manufacture,the selected oxidizing gas is formed into sub-micron size bubbles.

[0018] A quantity of diesel fuel having organic contaminants containedtherein, such as compounds of sulfur, is caused to flow into engagementwith the sub-micron size bubbles of oxidizing gas. The oxidizing gasbubbles are dispersed into the diesel fuel whereupon the sulfurcompounds contained within the oil are immediately oxidized, therebyforming sulfoxides and/or sulfones. The sub-micron size of the bubblesof the oxidizing gas greatly increases the surface area of the oxidizinggas/diesel fuel interface thereby substantially increasing theefficiency of the oxidizing reaction. Upon completion of the oxidationreaction, the sulfoxides and /or sulfones are removed from the dieselfuel by distillation or extraction.

[0019] Referring to FIG. 2 there is shown an apparatus 10 which may beutilized in the practice in the method of the invention. The apparatus10 includes a hollow tube 12 formed from sintered glass, sinteredceramic, or porous ceramic. Those skilled in the art will know andunderstand that other porous materials not subject to attack byoxidizing agents may be used in the practice of the invention. Thesintered/porous tube 12 is positioned within a tank 14.

[0020] An oxidizing gas is manufactured within a source 16 utilizingconventional and well known techniques. The oxidizing gas is preferablyozone, however, other oxidizing gases may be utilized in the practice ofthe invention if desired. Immediately upon its manufacture the oxidizinggas from the source 16 is directed into the interior of thesintered/porous tube 12 through piping 18.

[0021] Meanwhile diesel fuel having sulfur compounds initially containedtherein is caused to flow from a source 20 through piping 22 and thetank 14 to an outlet 24. The source 20 may comprise a conventionalreservoir, tank, etc., which receives diesel fuel from one or moresources.

[0022] The pressure of the oxidizing gas within in the interior of thesintered/porous tube 12 is maintained high enough to prevent diesel fuelcontained within the tank 14 from flowing inwardly through the tube 12into the interior thereof. Rather, oxidizing gas flows outwardly fromthe interior of the tube 12 and is formed into sub-micron size bubbleswhich are cleaved from the exterior surface of the sintered glass,sintered ceramic, or porous ceramic tube 12 by, and are dispersed in theflowing diesel fuel.

[0023] As the diesel fuel from the source 20 flows through the tank 14,it passes over the exterior surface of the sintered/porous tube 12thereby cleaving the sub-micron size bubbles of oxidizing gas from theexterior surface thereof. The sub-micron sized bubbles of oxidizing gasare immediately dispersed throughout the flowing fuel, whereupon organiccontaminants contained within the diesel fuel are immediately oxidizedinto sulfoxides and/or sulfones. It will be appreciated that because ofthe sub-micron size of the bubbles comprising the oxidizing gas thesurface area of the interface between the oxidizing gas and the dieselfuel is greatly increased, thereby greatly increasing the efficiency ofthe oxidizing reaction.

[0024] It is contemplated that all of the oxidizing gas will be consumedby the oxidizing reaction. If not, excess oxidizing gas may be recoveredfrom the diesel fuel through an outlet 26 and properly disposed of. Thediesel fuel is then directed to an apparatus 28 wherein the sulfoxidesand/or sulfones which were formed during the oxidation reaction areremoved from the diesel fuel either by distillation or by extraction.

[0025] An alternative apparatus 30 which may be utilized in the practiceof the method of the invention is illustrated in FIG. 3. The apparatus30 includes a sintered glass, sintered ceramic, or porous ceramic tube32 having a hollow interior which is supported within a tank 34 forrotation about its longitudinal axis. A motor 36 is positioned at oneend of the tank 34 and is operatively connected to the tube 32 to effectrotation thereof relative to the tank 34. An annulus 38 is located atone end of the tank 34 and is separated from the tank 34 and from themotor 36 by seals 40. A collar 42 connects the annulus 38 to theinterior of the sintered/porous tube 32 through a plurality ofpassageways 44.

[0026] In the operation of the apparatus 30 an oxidizing gas ismanufactured within a source 46 utilizing conventional and well knowntechniques. The oxidizing gas is preferably ozone and, however, otheroxidizing gases may be utilized in the practice of the invention.Immediately upon its manufacture the oxidizing gases directed into theannalus 38 through piping 48. From the annalus 38 the oxidizing gasflows into the interior of the sintered glass, sintered ceramic, orporous ceramic tube through the passageways 44 of the collar 42.

[0027] Diesel fuel received from a source 50. The source 50 may comprisea conventional reservoir or tank which receives the diesel fuel from oneor more sources.

[0028] Diesel fuel continuously flows from the source 50 through piping52 and through the tank 34 to an outlet 54. The pressure of theoxidizing gas within the hollow interior of the tube 32 is maintainedsufficiently high that diesel fuel flowing through the tank 34 does notflow inwardly through the tube 32 into the interior thereof. Rather,oxidizing gas from the source 46 flows outwardly from the interior ofthe sintered or porous tube 32 to the outer surface thereof.

[0029] The outwardly flowing oxidizing gas accumulates on the exteriorsurface of the sintered tube 32 in the form of sub-micron size bubbles.The sub-micron size bubbles of oxidizing gas are immediately cleavedfrom the exterior surface of the sintered tube by the flow of the dieselfuel over the exterior surface of the sintered/porous tube 32. Thesub-micron sized bubbles are dispersed throughout the flowing dieselfuel whereby the sulfur compounds initially contained within the flowingdiesel fuel are immediately oxidized into sulfoxides and/or sulfones.The sub-micron size of the bubbles of the oxidizing gas greatlyincreases the size of the interface between the oxidizing gas and theinitially contaminated liquid, thereby greatly increasing the efficiencyof the oxidation reaction.

[0030] Treated diesel fuel is recovered through the outlet 54. It iscontemplated that all of the oxidizing gas will be consumed by theoxidizing reaction. If not, excess oxidizing gas may be recovered fromthe treated liquid through an outlet 56 and thereafter properly disposedof. The diesel fuel flows into an apparatus 58 wherein the sulfoxidesand/or sulfones formed by the oxidation reaction are removed bydistillation or extraction. The treated diesel fuel is recovered atoutlet 59.

[0031] In the operation of the apparatus 30 shown in FIG. 4, theexterior surface of the tube 32 is rotated relative to the diesel fuelflowing through the tank 34 under the action of the motor 36. By thismeans the relative movement between the exterior surface of the tube 32and the diesel fuel flowing through the tank 34 is greatly increased.This in turn increases the number of sub-micron sized bubbles ofoxidizing gas which is dispersed into the flowing liquid, therebyincreasing the efficiency of the oxidation reaction.

[0032] An alternative apparatus 60 which may be utilized in the practiceof the method of the invention is illustrated in FIG. 4. The apparatus60 includes a sintered glass, sintered ceramic, or porous ceramic tube62 having a hollow interior which is supported within a tank 64 forrotation about its longitudinal axis. One or more turbines 66 aremounted on the sintered/porous tube 62 to effect rotation thereofrelative to the tank 64.

[0033] In the operation of the apparatus 60 an oxidizing gas ismanufactured within a source 76 utilizing conventional and well knowntechniques. The oxidizing gas is preferably ozone, however, otheroxidizing gases may be utilized in the practice of the invention.Immediately upon its manufacture the oxidizing gas is directed into theinterior of the sintered or porous tube 62.

[0034] Diesel fuel as received from a source 80. The source 80 maycomprise a conventional reservoir or tank which receives the diesel fuelfrom one or more sources.

[0035] Diesel fuel continuously flows from the source 80 through piping82 and through the tank 64 to an outlet 84. The pressure of theoxidizing gas within the hollow interior of the tube 62 is maintainedsufficiently high that diesel fuel flowing through the tank 64 does notflow inwardly through the tube 62 into the interior thereof. Rather,oxidizing gas from the source 76 flows outwardly from the interior ofthe tube 62 to the outer surface thereof.

[0036] The outwardly flowing oxidizing gas accumulates on the exteriorsurface of the sintered/porous tube 62 in the form of sub-micron sizebubbles. The sub-micron size bubbles of oxidizing gas are immediatelycleaved from the exterior surface of the sintered tube by the flow ofthe diesel fuel over the exterior surface of the tube 62. The sub-micronsized bubbles are dispersed throughout the flowing diesel fuel wherebythe sulfur compounds initially contained within the flowing diesel fuelare immediately oxidized into sulfoxides and/or sulfones. The sub-micronsize of the bubbles of the oxidizing gas greatly increases the size ofthe interface between the oxidizing gas and the initially contaminatedliquid, thereby greatly increasing the efficiency of the oxidationreaction.

[0037] Treated diesel fuel is recovered through the outlet 84. It iscontemplated that all of the oxidizing gas will be consumed by theoxidizing reaction. If not, excess oxidizing gas may be recovered fromthe treated liquid through an outlet 86 and thereafter properly disposedof. The diesel fuel flows into an apparatus 88 wherein the sulfoxidesand/or sulfones formed by the oxidation reaction are removed bydistillation or extraction. The treated diesel fuel is recovered atoutlet 90.

[0038] In the operation of the apparatus 60 shown in FIG. 5 the exteriorsurface of the sintered/porous tube 62 is rotated relative to the fuelflowing through the tank 64 under the action of the turbines 66. By thismeans the relative movement between the exterior surface of the sinteredtube 62 and the diesel fuel flowing through the tank 64 is greatlyincreased. This in turn increases the number of sub-micron sized bubblesof oxidizing gas which are dispersed into the flowing diesel fuel,thereby increasing the efficiency of the oxidation reaction.

[0039] Those skilled in the art will appreciate the fact that the use ofthe apparatus 30 shown in FIG. 3 or the apparatus 60 shown in FIG. 4provides certain advantages with respect to the use of the apparatusshown in FIG. 2 in the practice of method of the invention. When theapparatus 30 of FIG. 3 is utilized, the relative movement between theexterior surface of the sintered/porous tube 32 and the diesel fuelflowing through the tank 34 depends upon the operation of the motor 36rather than the flow rate of the liquid. This allows a greater number ofsub-micron size bubbles of oxidizing gas to be dispersed into the dieselfuel than would be possible if the cleaving of sub-microns sized bubblesof oxidizing gas from the exterior surface of the tube 32 depended uponthe flow of fuel alone. In this manner the efficiency of the oxidationreaction can be further increased.

[0040] When the apparatus 60 of FIG. 4 is utilized, the relativemovement between the exterior surface of the sintered/porous tube 62 andthe diesel fuel flowing through the tank 34 is greatly increased by theoperation of the turbines 66. This allows a greater number of sub-micronsize bubbles of oxidizing gas to be dispersed into the diesel fuel thanwould be possible if the cleaving of sub-microns sized bubbles ofoxidizing gas from the exterior surface of the tube 62 depended upon theflow of fuel alone. In this manner the efficiency of the oxidationreaction can be further increased.

[0041] Referring now to FIGS. 5 and 6, there is shown a method of andapparatus for improving the quality of diesel fuel 100 comprising asecond embodiment of the invention. In accordance with a secondembodiment of the invention, there is provided a tank 102 having aquantity of diesel fuel 104 contained therein. The diesel fuel issupplied to the tank 102 from a source 106 through piping 107.

[0042] A hollow disk 108 is mounted in the lower portion of the tank102. As is best shown in FIG. 6, the disk 108 includes a gas permeablepartition 110 supported on a tube 112 for rotation within the tank 102under the operation under the motor 114. The partition 110 may comprisesintered glass, sintered ceramic, or porous ceramic materials dependingupon the requirements of particular applications of the invention.Oxidizing gas received from a supply 116 is directed through piping 118and a suitable commutator 120 into the tube 112 and through the tube 112into the interior of the hollow disk 108. The tube 112 has a hollowinterior 121 and the disk 108 has a hollow interior 122 connected influid communication therewith.

[0043] The disk 108 is supplied with oxidizing gas at a pressure justhigh enough to overcome the head pressure of the water or other liquid104. The disk 108 is rotated by the motor 114 at an appropriate speed incontact with the diesel fuel 104 such that a shearing phenomen occurs atthe surface of the gas permeable partition 110 thus producing bubbles ofextremely small, i.e., sub-micron, size. The extreme small size of thebubbles thus produced results in a surface area to volume ratio of smallbubbles which significantly improves the efficiency of the oxidationreaction, in particular because the required vertical height of the tank102 and therefore the pressure of the gas is substantially reduced dueto the slower movement of the small bubbles in the liquid. The oxidizinggas reacts with sulfur compounds in the diesel fuel to form sulfoxidesand/or sulfones. Diesel fuel is recovered from the tank 102 throughoutlet 123 and any residual gas is recovered from the tank 102 throughoutlet 124. The diesel fuel is directed to an apparatus 126 wherein thesulfoxides and/or sulfones formed duration the oxidation reaction areremoved either by distillation or by extraction. The treated diesel fuelis recovered at outlet 128.

[0044] The method of improving the quality of diesel fuel comprised inthe present invention may be used either as the sole process fortreating diesel fuel or in combination with existing hydrotreatingtechniques. The method of the present invention totally removes sulfurcompounds from diesel fuel, thereby improving the cetane rating of thediesel fuel. In particular, when the method of the present invention isused subsequently to hydrotreating, the aromatic compounds which remainafter the hydrotreating process are removed thereby increasing thecetane rating of the diesel fuel.

[0045] Although preferred embodiments of the invention have beenillustrated in the accompanying Drawings and described in the foregoingDetailed Description, it will be understood that the invention is notlimited to the embodiments disclosed, but is capable of numerousrearrangements, modifications, and substitutions of parts and elementswithout departing from the spirit of the invention.

I claim:
 1. A method of removing sulfur compounds from diesel fuelcomprising the steps of: providing an oxidizing gas; forming theoxidizing gas into sub-micron size bubbles; providing a flow of dieselfuel; dispersing the sub-micron size bubbles of oxidizing gas into theflowing diesel fuel thereby oxidizing the sulfur compounds initiallycontained within the diesel fuel into sulfoxides and/or sulfones;removing the sulfoxides and sulfones from the diesel fuel; andrecovering the treated diesel fuel.
 2. The method of claim 1 wherein theoxidizing gas is ozone.
 3. The method of claim 2 wherein at least partof the oxidizing gas is formed into sub-micron size bubbles anddispersed into the flowing diesel fuel immediately upon its manufacture.4. The method according to claim 1 wherein: the oxidizing gas isdirected through sintered material to an exterior surface; and theflowing diesel fuel is directed across the exterior surface therebycleaving sub-micron sized bubbles of oxidizing gas from the exteriorsurface.
 5. The method according to claim 4 including the additionalstep of moving the exterior surface relative to the flowing diesel fuel.